1. Field
This invention relates generally to the art of lubrication and more particularly to a novel passive lubricating method and system for supplying lubricating oil to surfaces to be lubricated.
2. Prior Art
Effective lubrication of bearing surfaces is essential in most if not all machines. This is particularly true of machines destined for operation in space. In this case, the lubricating system must be designed to remain effective and operable without attention for the entire intended lifetime of the space machine. This lifetime may be ten years or more. One example of such a lubrication requirement involves the lubrication of the bearings for the despun platform of a dual-spin spacecraft.
In this regard, it will be understood that the space environment presents a rather hostile environment for lubricating systems. This is due not only to the temperatures and temperature fluctuations encountered but also to the vacuum of the environment which tends to cause relatively rapid evaporation of lubricating oil from the bearing surfaces being lubricated. Such evaporation is minimized by using lubricating oils having as low a vapor pressure as possible. Even then, however, some type of lubricating system must be provided for maintaining an adequate supply of lubricant to the bearing surfaces over the entire operating lifetime of the spacecraft without flooding of the surfaces with oil.
Lubricating systems for these purposes are commonly classified as passive and active systems. An active lubrication system is one in which some type of mechanically or electrically produced force is utilized to induce flow of lubricant from a lubricant reservoir or the like to the bearing surfaces to be lubricated. In a passive lubrication system, this lubricant flow is induced by natural forces, such as capillary forces.
One type of passive spacecraft bearing lubrication system in current use comprises a porous oil reservoir in the form of a porous nylon block or the like saturated or impregnated with oil. This reservoir is placed near or in contact with the surfaces to be lubricated and is designed to supply oil to the surfaces by evaporation from the reservoir and condensation on the bearing surfaces. Means are provided to regulate the replenishment rate at which oil is condensed on the bearing surfaces so as to maintain the proper amount of lubricant on the surfaces.
Such porous nylon reservoir type lubrication systems, however, have an inherent defect which this invention is intended to overcome. Thus, recent studies have demonstrated that if incompletely filled or saturated with oil, such porous nylon blocks, rather than dispensing oil to the bearing surfaces, actually imbibe or absorb oil. In other words, they function as oil sinks rather than oil reservoirs. Accordingly, this type of passive lubricating system is ill-suited to or totally incapable of use for spacecraft bearing lubrication.
This deficiency of the porous nylon oil reservoir is believed due to the fact that nylon is an oleophillic material, that is a material which is wetted by oil. As a consequence, capillary forces tend to suck oil into the reservoir.